Don't render "Comment T1#1" links on previews

Summary:
I somehow missed this, we render silly nonsense in the comment previews right
now. Don't render these links if we're rendering a preview.

Test Plan:
Looked at comment previews, less nonsense.

Reviewed By: tuomaspelkonen
Reviewers: aran, jungejason, tuomaspelkonen
CC: aran, tuomaspelkonen
Differential Revision: 388